The transition metal catalyzed epoxidation of ethylenically unsaturated substrates using organic hydroperoxides as oxidants is a well known method for the preparation of epoxides. In one variation of this technology, optically active epoxy alcohols are prepared by reacting allylic alcohols with organic hydroperoxides in the presence of transition metal catalysts containing chiral ligands. The optically active epoxy alcohol products are of great value as intermediates in the synthesis of compounds having high physiological activity.
However, the recovery of epoxy alcohols from crude epoxidation reaction mixtures is complicated by the numerous components typically present in such mixtures. The reaction mixture will normally contain the epoxy alcohol, unreacted organic hydroperoxide (usually used in excess), unreacted allylic alcohol, transition metal catalyst, the organic alcohol coproduct derived from the reacted hydroperoxide, and solvent. Epoxy alcohols tend to be highly reactive and susceptible to decomposition at elevated temperatures, particularly in the presence of Lewis acids such as the transition metal compounds typically used as catalysts in epoxidation reactions.
Methods have been developed for the recovery of water-soluble non-crystalline epoxy alcohols such as glycidol. Such methods are described, for example, in U.S. Pat. No. 3,374,153 and USSR Inventor's Certificate No. 480,695. However, these methods are generally not suitable for the recovery of water-insoluble crystalline epoxy alcohols since they rely on either extracting the epoxy alcohol into an aqueous phase or distillation of the epoxy alcohol. Water-insoluble epoxy alcohols tend to be significantly higher in molecular weight and lower in volatility than the water-soluble epoxy alcohols and thus cannot be readily distilled without significant decomposition taking place.
Sharpless [J. Am. Chem. Soc. 109, 5765(1987)] teaches the purification of water-insoluble crystalline epoxy alcohols by various multi-step procedures. These procedures are not readily adaptable to commercial epoxy alcohol production due to either inherent safety hazards, the use of large quantities of materials such as magnesium sulfate and diatomaceous earth, or the tedious nature of the several steps required.
Clearly, there is a need for a practical, economical method whereby a water-insoluble crystalline epoxy alcohol may be separated from an epoxidation reaction mixture.